1. Field of the Invention
The present invention relates to a fusing device which fuses a toner image on a printable medium and an image forming apparatus having the same, and more particularly, to a fusing device which electrifies a printable medium to enhance fusing efficiency to a toner image and an image forming apparatus having the same.
2. Description of the Related Art
In general, an image forming apparatus of an electro-photographic type forms an electrostatic latent image on an image support, such as, a photosensitive body, electrified at a predetermined electric potential through exposure, develops such a latent image with toner, and transfers and fuses a toner image onto a printable medium to form an image.
A fusing device is typically provided in a printing path of such an image forming apparatus, to fuse a toner image on the printable medium under heat and pressure, i.e., toner is melted and bonded to the printable medium by heat and pressure rollers.
FIG. 1 illustrates a fusing device 10 of a typical image forming apparatus. Referring to FIG. 1, the fusing device 10 includes a fusing roller 20 in which a heat source (not shown) is provided, and a pressing roller 30 which is disposed opposite to the fusing roller 20 and is elastically pressed toward the fusing roller 20 by an elastic member 31 to fuse a toner image on a printable medium.
Generally, a surface of the fusing roller 20 is heated by heat from the heat source 21. When a printable medium M on which a toner image T is transported to the fusing device 10, the printable medium M passes a fusing nip N1 which is formed between the fusing roller 20 and the driving roller 30. Here, the toner image T is fused onto the printable medium M by heat and pressure, thereby completing a fusing process.
Recently, as a printing speed of an image forming apparatus increases, and time when the printable medium passes through the fusing device decreases, fusing efficiency can also be decreased. In particular, if charge per mass of toner is low, an adhesive force to the printable medium becomes weak. Moreover, if moisture in the printable medium is evaporated, a toner which is adhered to the printable medium is removed to the outside, thereby causing a so-called line burst phenomenon. In this case, the toner is removed here and there on the printable medium, thereby causing an inconvenience to a user.